Many products of commercial value need to be protected against counterfeiting, forging and copying. To this end, products of high value, such as perfumes or watches, as well as documents of value, such as banknotes, tax stamps, credit cards etc., are typically provided with security elements.
Typical security elements include for instance holograms, markings with luminescent dyes or pigments emitting in the visible spectrum upon excitation by e.g. UV radiation, watermarks, or graphical elements using a specific kind of pigment that is not easily available and/or which provides an optical impression by a specific orientation of the pigment that is difficult to achieve with commercially available equipment. An example of the latter is e.g. the so-called “rolling bar” effects that can be provided by orienting magnetic non-spherical particles.
A drawback of such security elements is that they may be relatively easy to reproduce and/or are not machine-readable. Further, the security elements are typically provided in an identical manner on products of the same type, so that they cannot be used to identify a specific product and cannot be used to distinguish between different products of the same type. This is however desirable in many commercial fields, as this allows to track a product over the distribution chain to identify stolen goods.
In order to solve these problems, the prior art suggests using specific kinds of codes, such as alphanumeric product verification codes, barcodes or QR codes. However, the problem of such codes is that the information contained therein can be easily decoded. It is further possible for counterfeiters to predict, within certain boundaries, a code that could be considered authentic, as the algorithms used for the production of such codes are in the public domain or can be obtained by analysing the information provided on a series of authentic products.
In order to address these problems of pre-designed codes, the prior art suggests using random distribution features that are unique for each product and stored in a database, to thereby allow to identify a product as genuine by comparison with database entries. The random distribution forms a security feature that cannot be predicted, as it is not a pre-designed code.
One document describing such a technology is GB 2 324 065 A, which describes an identification code for banknotes or credit cards comprising a pattern of random beads in a plastic matrix. The position of the beads inside the plastic matrix is unique for each product, such as credit card or banknote, and e.g. the position of a sequence of beads above or below a line represents the ones and zeroes in a binary code that is used for identifying the product.
A similar technology is described in EP 1 953 684 A1, which describes an authentication means including a random arrangement of stains. This document describes that such a unique arrangement of stains can be obtained e.g. by spraying an ink, which can be conventional or covert such as to be detectable only under specific illumination conditions. The random arrangement of stains forms a machine-readable code that can be read out by image processing, forming a descriptor or data set that corresponds to the stains arrangement. A related technology using invisible taggants that are randomly positioned inside a material as matrix, forming a random pattern that can be used for authentication by comparison with a database, is described in U.S. Pat. No. 7,687,271 B2.
A common problem of all the technologies described above is that the formation of the arrangement of stains or taggants, and subsequently the registration of the resulting pattern, is performed in a database at a single place, i.e. a place of manufacture. Nowadays many commercial goods are however prepared in multi-step processes performed at different sites or by different manufacturers. One example is the production of a jet engine where the blades of the turbine may be prepared from a specific highly resistant material produced at a first site, and the engine is assembled at another site by qualified mechanics. In such a case, it would be desirable to have available a means for securing that the right material has been used and that the assembly has been correctly conducted. A security element providing authentication for either one of these will not be sufficient to prove both, and a single security element clearly identifying a specific produced item and capable of tracing the course of manufacture in a simple, yet unique manner is desired.